Stellar abundances and ages for metal-rich  Milky Way globular 
clusters

Feltzing, Sofia; Primas, F.; Johnson, Rachel

doi:10.1051/0004-6361:200810137

Cited by 28 publications

(32 citation statements)

References 98 publications

(133 reference statements)

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“…The method differs slightly from its most common implementation in the literature where an iterative scheme is employed and one parameters is varied in each step (see, e.g., Drake 1991; Drake & Smith 1991, and discussions therein). Instead, the usage of SME in fully free mode is more akin to the method used in Feltzing et al (2009) where the parameter space is searched (by hand) for a best fit to all criteria simultaneously.…”

Section: Methods 1: Fe I and Fe Ii Linesmentioning

confidence: 99%

Determination of robust metallicities for metal-rich red giant branch stars

Liu

Ruchti

Feltzing

et al. 2017

A&A

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Context. The study of the Milky Way relies on our ability to interpret the light from stars correctly. With the advent of the astrometric ESA mission Gaia we will enter a new era where the study of the Milky Way can be undertaken on much larger scales than currently possible. In particular we will be able to obtain full 3D space motions of red giant stars at large distances. This calls for a reinvestigation of how reliably we can determine, e.g., iron abundances in such stars and how well they reproduce those of dwarf stars. Aims. Here we explore robust ways to determine the iron content of metal-rich giant stars. We aim to understand what biases and shortcomings widely applied methods suffer from. Methods. In this study we are mainly concerned with standard methods to analyse stellar spectra. This includes the analysis of individual lines to determine stellar parameters, analysis of the broad wings of certain lines (e.g., Hα and calcium lines) to determine effective temperature and surface gravity for the stars. Results. For NGC 6528 we find that [Fe/H] = +0.04 dex with a scatter of σ = 0.07 dex, which gives an error in the derived mean abundance of 0.02 dex. Conclusions. Our work has two important conclusions for analysis of metal-rich red giant branch stars. 1) For spectra with S/N below about 35 per reduced pixel [Fe/H] become too high, 2) Determination of T eff using the wings of the Hα line results in [Fe/H] values about 0.1 dex higher than if excitational equilibrium is used. The last conclusion is perhaps not surprising as we expect NLTE effect to become more prominent in cooler stars and we can not use the the wings of the Hα line to determine T eff for the cool stars in our sample. We therefore recommend that in studies of metal-rich red giant stars care needs to be taken to obtain sufficient calibration data in order to be able to also use the cooler stars.

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Section: Methods 1: Fe I and Fe Ii Linesmentioning

confidence: 99%

Determination of robust metallicities for metal-rich red giant branch stars

Liu

Ruchti

Feltzing

et al. 2017

A&A

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“…Based on high-resolution spectra of eight stars, Cohen (1983) found this cluster to be +0.38 dex more metal rich than 47 Tuc. re-analysed equivalent width measurements of Gratton (1987) No study dedicated to light elements was carried out to our knowledge, so the hint by Feltzing et al (2009) is our only comparison. We do find a clear and bimodal CH and CN anticorrelation, which is even more striking if one considers the low number of stars observed and the relatively low S /N around 3900 Å.…”

Section: Ngc 6352mentioning

confidence: 99%

Low-resolution spectroscopy of main sequence stars belonging to 12 Galactic globular clusters

Pancino

Rejkuba²,

Zoccali

et al. 2010

A&A

164

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Context. Globular clusters show star-to-star abundance variations for light elements that are not yet well understood. The preferred explanation involves a self-enrichment scenario, within which two subsequent generations of stars co-exist in globular clusters. Observations of chemical abundances in the main sequence and sub-giant branch stars allow us to investigate the signature of this chemically processed material without the complicating effects caused by stellar evolution and internal mixing. Aims. Our main goal is to investigate the carbon-nitrogen anti-correlation with low-resolution spectroscopy of 20−50 stars fainter than the first dredge-up in seven Galactic globular clusters (NGC 288, NGC 1851, NGC 5927, NGC 6352, NGC 6388, and Pal 12) with different properties. We complemented our observations with 47 Tuc archival data, with four additional clusters from the literature (M 15, M 22, M 55, NGC 362), and with additional literature data on NGC 288. Methods. In this first paper, we measured the strengh of the CN and CH band indices, which correlate with the N and C abundances, and we investigated the anti-correlation and bimodality of these indices. We compared r CN , the ratio of stars belonging to the CN-strong and weak groups, with 15 different cluster parameters. Results. We clearly see bimodal anti-correlation of the CH and CN band stregths in the metal-rich clusters (Pal 12, 47 Tuc, NGC 6352, NGC 5927). Only M 15 among the metal-poor clusters shows a clearly bimodal anti-correlation. We found weak correlations (sligthly above 1σ) of r CN with the cluster orbital parameters, present-day total mass, cluster concentration, and age. Conclusions. Our findings support the self-enrichment scenario, and suggest that the occurrence of more than two major generations of stars in a GGC should be rare. Small additional generations (<10−20% of the total) would be difficult to detect with our samples. The first generation, which corresponds to the CN-weak stars, usually contains more stars than the second one ( r CN = 0.82 ± 0.29), as opposed to results based on the Na-O anti-correlations.

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“…Several projects designed to obtain this general view of the GB are either ongoing or planned for the near future (e.g. Minniti et al 2010;Feltzing 2011;Ness & Freeman 2012;Elia Garcia Perez et al 2012). The interpretation of these observations is inhibited by variations in the dust extinction properties on small scales towards the different GB regions.…”

Section: Introductionmentioning

confidence: 99%

Reddening and metallicity maps of the Milky Way bulge from VVV and 2MASS

Gonzalez

Rejkuba

Zoccali

et al. 2012

A&A

329

505

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Context. The Milky Way bulge is the nearest galactic bulge and the most readily accessible laboratory for studies of stellar populations in spheroids based on individual stellar abundances and kinematics. These studies are challenged by the strongly variable and often large extinction on a small spatial scale. Aims. We use the Vista Variables in the Via Lactea (VVV) ESO public survey data to measure extinction values in the complete area of the Galactic bulge covered by the survey at high resolution. Methods. We derive reddening values using the method described in Paper I. This is based on measuring the mean (J − K s ) color of red clump giants in small subfields of 2 × 2 to 6 × 6 in the following bulge area:• . To determine the reddening values E(J − K s ) for each region, we measure the RC color and compare it to the (J − K s ) color of RC stars measured in Baade's Window, for which we adopt E(B − V) = 0.55. This allows us to construct a reddening map sensitive to small-scale variations minimizing the problems arising from differential extinction. Results. The significant reddening variations are clearly observed on spatial scales as small as 2 . We find good agreement between our extinction measurements and Schlegel maps in the outer bulge, but, as already stated in the literature the Schlegel maps are unreliable for regions within |b| < ∼ 6• . In the inner regions, we compare our results with maps derived from DENIS and Spitzer surveys. While we find good agreement with other studies in the corresponding overlapping regions, our extinction map is of higher quality owing to both its higher resolution and a more complete spatial coverage of the bulge. We investigate the importance of differential reddening and demonstrate the need for high spatial resolution extinction maps for detailed studies of bulge stellar populations and structure. Conclusions. We present the first extinction map covering uniformly ∼315 sq. deg. of the Milky Way bulge at high spatial resolution. We consider a 30 arcmin window at a latitude of b = −4• , which corresponds to a frequently studied low extinction window, the so-called Baade's Window, and find that its A Ks values can vary by up to 0.1 mag. Larger extinction variations are observed at lower Galactic latitudes. The extinction variations on scales of up to 2 −6 must be taken into account when analyzing the stellar populations of the Galactic bulge.

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Stellar abundances and ages for metal-rich Milky Way globular clusters

Cited by 28 publications

References 98 publications

Determination of robust metallicities for metal-rich red giant branch stars

Determination of robust metallicities for metal-rich red giant branch stars

Low-resolution spectroscopy of main sequence stars belonging to 12 Galactic globular clusters

Reddening and metallicity maps of the Milky Way bulge from VVV and 2MASS

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